1. Field of the Invention
The present invention relates to a manufacturing method of colored diamond and, more particularly, to a manufacturing method of colored diamond by ion implantation and heat treatment.
2. Description of the Prior Art
Generally, natural diamonds are collected in a wide range from a colorless state to a black color. Among the diamonds, a colorless diamond without impurities has the highest value and a diamond having a rare color has a higher value. However an artificially synthesized diamond for industrial use contains impurities such as materials used as catalysts, and thereby has a certain color. The artificial diamond has high hardness and acid-resistance, however the value of diamond as a jewel is far low. Accordingly, a method to solve the aforementioned problems has been developed by artificially coloring the low-valued natural and artificial diamonds using the technique described herein.
A conventional diamond coloring method includes radioactive irradiation, surface diffusion, and ion implantation.
Firstly, The radioactive irradiation utilizes the principle of coloring the non-metal gemstones by radiating high-energy particles onto the surface of the gemstones to induce point defects in the sub-surface to deeper inside from the surface of the gemstones. However the radioactivity is continuously emitted from the non-metal gemstones, and this method has a disadvantage that it takes a long period more than 10 years until the radioactivity is reduced to a safe level, considering the half-life period of the radioactive material.
It is reported that diamond color may change from pale yellow to fancy blue, green, brown, orange, very dark green, and yellow by collision with a high-energy particle such as electron, neutron, proton, gamma-ray, and alpha-particle. When the diamond is exposed to a gamma-ray (generally using 60Co), a blue or yellow color center is formed in the diamond having a brown or brownish green color appearance. Alternatively when the diamond is irradiated by an electron beam called Linac treatment, the diamond has a deep blue color, and an undesirable residual yellow color may be removed by the post-irradiation heat treatment. A blue color ranging from medium to dark-grayish blue may be obtained by irradiating the diamond by high-speed neutrons in a nuclear power reactor, and this color is named steely or inky. It is reported that the color remains for a long period even without the post-irradiation heat treatment. In the case of coloring a diamond in a nuclear power reactor, installation of Linac treatment and commercial transaction of the diamond need an approval of NRC regulation due to the radioactivity. A dark blue color may be obtained by complex processing of treatment in the nuclear power reactor, Linac treatment, and heat diffusion treatment. The color obtained by this process is named Electra blue, Super blue, New blue, Swiss blue, Max blue, American blue, or Super sky blue.
However, except the gamma-ray and neutron irradiation, the radioactive irradiation generally changes the color close to the surface of diamond and causes umbrella-like color zonation or irregular coloring.
Secondly, surface diffusion technique is a method to diffuse gaseous elements from the surface by heating the diamond in a furnace, where the gaseous metal elements may be applied in the circumference of diamond in the form of powder or liquid, and the diamond is heated up to a specific temperature. This method has an economical advantage that only a high temperature furnace avoiding oxidation of metal diffusates is required. However the method has a problem that differences in the diffusion rates due to the different crystallographic directions of the surfaces may cause irregular color changes, and the color changes are as little as it is unable to identify even with the naked eye in the case of a small jewel such as diamond. The method utilizes color development by coating and then baking, and the color may be nicely changed, if the coated layer is very sound. However, this method has a disadvantage that the appearance of jewel becomes to look bad and the color returns to its initial state, when the coated layer is worn out or peeled off.
In some instances, the diamond color is changed to colorless, pale pink, or pale blue by heating the diamond under high pressure to remove or to reduce the color centers. This method has been developed by GE, and the diamonds produced by this method is being sold by Pegasus Overseas Limited (POL), with a name of “GE POL”.
Lastly, ion implantation is a method to implant metal ions accelerated under high vacuum to the surface of diamond, and has a characteristic that various color development are possible according to the kinds of ion. However this method has a disadvantage that an expensive ion implantation equipment is required and the depth of ion implantation is less than 1 μm, final color appearance of the diamond is inferior to that of natural diamond, and surface damage occurs during implantation.